Electrical alarm system

ABSTRACT

A plurality of protected stations connected by transmission lines to a central monitoring station. Each protected station has a condition sensing device capable of transmitting an abnormal condition signal to the monitoring station where all the protected stations are simultaneously monitored by a master signal detector. The monitoring station also has an individual signal detector and a selector switch so that an abnormal condition signal from any particular protected station may be monitored by the individual detector in exclusion of all the other protected stations which are monitored by the master detector.

AU 1w we 3D 91H, UH R r 2 o ar o w .LYK Ni a 3 01 w s 3 e w e, e 3. Q, x

[ ELECTRICAL ALARM SYSTEM 2/1967 5/1970 Titherington....

[72] Inventor: Francis A. Scott, 863 Orange 5/1955 Schmidt...............................340/261 Avenue, Daytona Beach, Fla. 32014 Feb. 11, 1972 Appl. No.2 225,401

Primary Examiner-John W. Caldwell Assistant Examiner-Robert J. Mooney Attorney-Munson H. Lane et a1.

[22] Filed: [211 [57] ABSTRACT A plurality of protected stations connected by trans- Related [1.8. Application Data [63] Continuation-impart of Ser. No. 851,895, Aug. 21,

1969,abandoned.

mission lines to a central monitoring station. Each protected station has a condition sensing device capable of transmitting an abnormal condition signal to the [52] US. Cl.............,.34G/412, 340/258 R, 340/261, 179/1 H, 179/1 MN monitoring station where all the protected stations are [51] int. [58] Field of Search..340/412, 258 R, 261, 276, 148;

simultaneously monitored by a master signal detector. The monitoring station also has an individual signal detector and a selector switch so that an abnormal condition signal from any particular protected station may be monitored by theindividual detector in exclusion of all the other protected stations which are monitored by the master detector.

179/1 R, 1 H, 1 MN References Cited UNITED STATES PATENTS 4/1969 McKinzie........................

18 Claims, 8 Drawing Figures 111 ll ll l.illilllllllliilillllllJ a a M A T a a s a a L who T 4 ago R W m .H mm m i E H 1 2 w Hw M .O A 4 3 2 T r. f w a a E .m 2 6 N J D 0 T IL R W M m w n m w wmlm .n. m T WM M M 7,1 .W L e r e r L om m PATENTEDUEC 5 I972 MASTER SPEAKER AM PLIFIER SHEET 3 0F 6 F/ 6. 4.

INDIVIDUAL SPEAKER AMPLl FtER Txa em: MODULE #3 K I M Z :2%r

{x2 SITE MODULE #2 M| T0 6.3 VAC.

llllllelllllllllulllloilllulli lllllllll'llllnl PATENTEDBEB 5:912

SHEET 8 OF 6 QQ 3 E N;

IUPZ m mokomJum 20mm 0534 mst ELECTRICAL ALARM SYSTEM This application is a continuation-in-part of my earlier filed pending application Ser. No. 85l,895, filed Aug. 21 1969 now abandoned.

This invention relates to new and useful improve ments in electrical alarm systems of the general type in which a plurality of protected stations are connected by transmission lines to a central monitoring station so that abnormal conditions such as burglaries, fires, holdups, or the like, occuring at the protected stations may be signalled to and detected at the monitoring station.

In conventional systems of this general type the monitoring station requires separate detecting equipment for each protected station, thus involving a duplication of components, higher cost, larger space, and some measure of coordination and dexterity on the part of the attendant in dealing with the separate detecting equipment of the several protected stations which are being monitored.

The principal object of the invention is to avoid the above outlined disadvantages of conventional systems, this being attained by providing the monitoring station with a master signal detector which simultaneously monitors all the protected stations, and also with an individual signal detector and a selector switch so that when the abnormal condition signal originating at any particular protected station is detected by the master detector, an appropriate actuation of the selector switch will transfer that signal to the individual signal detector where the abnormal condition at that particular protected station may be individually monitored, in exclusion of all the other protected stations which continue to be monitored by the master signal detector.

Thus, undue duplication of components is eliminated in terms of it not being necessary to provide separate detecting equipment of each individual protected station. Also, the equipment costs and space requirements are kept low, and the task of the attendant at the monitoring station is considerably simplified.

With the foregoing more important objects and features in view and such other objects and features which may become apparent as this specification proceeds, the invention will be understood from the following description taken in conjunction with the accompanying drawings, wherein like characters of reference are used to designate like parts, and wherein:

FIG. 1 is a block diagram broadly showing the relationship of multiple remote protected areas with a cen- .tral monitoring unit; I

FIG. 2 is a front elevational view of the central monitor unit display panel showing the master detector, individual detector, selector switch and indicator lights at the central monitoring station;

'FIG. 3 is a partial schematic and partial block diagram of one of the remote protected stations;

FIG. 4 is a partial schematic and partial block diagram of the central monitor station;

FIG. 5 is a schematic diagram of the power supply for the central monitor;

FIG. 6 is a schematic diagram showing the individual lamps indicating which remote stations are turned-on and the remote station test switches located at the monitor station;

FIG. 7 is a schematic diagram of the components contained within each individual site module located at the monitor station; and

FIG. 8 is a schematic diagram of the amplifier circuits for the individual and master loud speakers. Only one circuit is shown but two separate similar circuits are required.

Referring now to the accompanying drawings in detail, the electrical alarm system of the invention comprises a plurality of remote protected stations which are connected by transmission lines to a central monitoring station. For illustrative purposes, five of the remote protected stations, designated generally as 10 in FIG. 1 are connected by transmission lines 12 to a remote monitoring station 14, it being understood that several, perhaps ten, twenty or more, protected stations such as the station 10, are connected to the same monitoring station 14 by additional transmission lines. For all practical purposes, the transmission lines 12 are leased telephone lines, so that the use of special lines is not necessary for purposes of the invention.

In each of the protected stations 10 a condition sensing device is included which is capable of being monitored and is also capable of transmitting a signal to the monitoring station 14 when some type of an abnormal condition comes into being at the protected station, as for example, a burglary, a fire, a hold-up, or the like.

The monitoring station 14, shown in block diagram in FIG. 1 and having an instrument panel portion 14a thereof shown in,elevation in FIG. 2, includes a master signal detector 15 which monitors the condition sensing devices of all of the protected stations 10 at the same time, and it also includes an individual signal detector 16 and a manually operable selector switch 17, arranged so that when any particular one of the protected stations 10 sends an abnormal condition signal which is detected by the master detector 15, that signal may be transferred by an appropriate actuation of the selector switch 17 to the individual detector 16 in order that the abnormal condition signal of that particular station may be monitored individually by the detector 16, in exclusion of all the other protected stations which continue to be monitored simultaneously by the master signal detector 15. The instrument panel portion 14a of the monitoring station 14 also includes a plurality of indicator lights 18, one for each of the protected stations 10, and the circuit arrangement at the monitoring station is such that when an abnormal condition signal is received at the master signal detector 15 from any one of the protected stations 10, the appropriate indicator lamp 18 of that protected station becomes energized and thus alerts the attendant of the monitoring station 14 to the fact that an abnormal condition exists at a particular protected station. Conveniently, this visual alert may be accompanied by an audible alert, for example from a buzzer, which becomes energized with any one of the indicator lamps 18.

In any event, the attendant at the monitoring station 14 then proceeds to actuate the manual selector switch 17, which has a plurality of settings corresponding to the respective protected stations and also to the respective indicator lamps 18, so that when an abnormal condition signal is received by the master detector 15 and the protected station sending that signal is identified by energization of one of the indicator lamps 18, the attendant turns the selector switch 17 to the appropriate setting of the protected station as indicated by the corresponding lamp. This causes the abnormal condition signal from that particular station to be transferred from the master detector to the individual detector 16, where that signal may be individually'monitored in exclusion of all the other protected stations which continue to be monitored simultaneously on the master detector 15.

it may be noted at this point that although the signal transfer from the master detector 15 to the individual detector 16 is effected by manual actuation of the selector switch 17 as prompted by energization of one of the indicator lights 18, the same operation may be made automatic by utilizing the same signal which energizes one of the indicator lights 18 to also actuate a suitable relay circuit by which the selector switch 17 automatically responds to transfer the signal of a particular protected station from the master detector 15 to the individual detector 16.

Referring now to FIG. 3 each protected remote station 10 such as a home, store, office, school, etc. which is being monitored includes one or more microphone sound pickups 20 located within the remote station for detecting sound produced within the range of the microphones. Sound picked up by the microphones is amplified in an amplifier 21 which may include one or more audio amplifier stages of conventional type. The audio output from the amplifier 21 is coupled by means of a coupling transformer 37 and a Y-pad 38 to a pair of leased telephone lines 12 extending between the remote station and the monitor station subsequently to be described. The amplifier 21 is powered from an AC to DC power supply 28 of a conventional type which receives AC current from a 117 volt AC source through a fuse F1 in one leg and through one section 300 of a double pole activate switch 30. When the activate switch 30 is closed, the power supply 28 is energized and converts AC to DC for supply of the amplifier 21 and various devices to be described.

' For the purpose of testing the operative condition of the remote station from the monitor station 14 an audio noise generator 40, which will also be referred to as a Sonalert, is connected in circuit with the power supply 28 and a relay switch 39a. The energizing coil 39 of the relay switch is connected on one side to a second section 30b of the activate switch 30 and'from there to ground, and the other side is connected through a center tap 370 on the secondary side 37b of coupling transformer 37, the conductors 41, telephone lines 12 to line transformer 22 at the monitor station 14 (See H6. 4) from whence it is connected by means of a center tap on the primary side of the line transformer 22 through a normally open test switch (See FIG. 6) to a a 91 volt DC bus at the monitor station 14. When it is desired to test the operativeness of the microphones 20 and amplifier 21 at a remote station the operator at the monitor station 14 actuates the test switch associated with the selected remote station which'energizes the relay coil 39 and closes the circuit to the Sonalert device 40. The Sonalert device 40 produces an audible sound which is picked up by the microphones 20, amplified and transmitted from the remote station 10 over the leased lines 12 to the monitor station 14 where the sound is monitored in a manner subsequently to be described.

Also present at the remote station may be various auxiliary devices including an emergency alarm overide switch 29, and several means for detecting and signalling various abnormal conditions such as fire, temperature, burglary etc. The emergency alarm overide switch 29 is provided so that someone at the remote station may signal to the monitor station 14 merely by depressing the emergency alarm overide switch 29. The switch 29 is in circuit with a 6 volt battery source 28' which energizes an oscillator 32 to produce a three thousand Hertz signal which is coupled through a coupling transformer 42, the Y-pad 38 and the telephone lines 12 to the monitor station 14.

Connected in parallel circuit with the normally open switch 29 are a plurality of diverse condition sensing and encoding circuits. A fire condition sensing circuit includes the tire sensing switch 330 and a fire alarm encoder 33 driven by a 12 rpm DC motor 33b. The encoder 33 is a rotary switch having an annular rotary conductor ring 33' which is continuously wiped by a brush contact 33" connected to one side of the sensing switch 330. An arcuate conductor segment projecting radially from the conductor ring 33"successively engages the fixed contacts which are equally spaced in an annular ring about the annular conductor 33'. The arcuate segment 33c is long enough so that it will bridge a pair of adjacent fixed contacts 33d simultaneously so that the segment 33c will always be in contact with one of the fixed contacts 33d as it rotates through 360. By contacting various of the fixed contacts to theother side of the circuit from the sensing switch 34a and leaving other of the fixed contacts vacant, it will be apparent that different code patterns maybe established based on successive pulse code patterns wherein the pulses are of various widths and are variously spaced. The encoder 33 is connected to produce a dash-dash code of equally spaced pulses of equal prolonged pulse width. v

The other encoders 34 and 35 are similar to the encoder 33 except that they are connected to produce a different pulse-pattern. They each have a condition sensing switch 34a and 35a associated with the encoders 34 and 35 respectively. The encoder 34, which is designated a temperature alarm encoder is connected to produce a code of successive dot-dash-dotdash pulses; The encoder 35 which is designated other" is connected to produce dash-dot-dash pulse sequences. The sensing switches 33a, 34a and 350 are selected according to the condition which they are intended to sense and maybe of various types well known in the art. The tire and temperature sensing switches may be thermostats of various temperature settings adapted to close circuits when temperatures are too high, or if the temperature has too rapid a rate of rise. Any number of condition sensing circuits may be included as desired. The condition sensing switch 36 which may be closed in response to the misplacement of an object during a burglary attempt will produce a continuous signal when closed.

The condition sensing switches and their respective encoders being parallel connected in the energizing circuit of the 3KHZ oscillator effectively key the oscillator when activated in response to an abnormal condition so that the oscillator produces a pulse coded output of audible frequency. The 6 volt battery 28' is common to all of the'encoders. The relays 43,44 and 45 having their energizing coils connected in parallel with the encoder drive motors 33b, 34b and 35b respectively and having their movable contacts 43a, 44a and 45a connected in circuit between the encoders 33, 34 and 35 respectively and the oscillator 32 are provided so that the alarms will not sound if the encoder motors stop on a contact position. The relays 43, 44 and 45 will normally open their respective encoder circuits when the associated motors 33b, 34b and 35b are de-energized, but will close their respective encoder circuits when the associated motors are energized.

Turning now to the monitor station as shown in FIG. 4 it will be seen that transmission lines 12 from each protected station connect with an individual site module 47 of which there are several identical modules corresponding in number with'the number of protected remote stations 10. Since the site modules 47 are identical, only one will be described. The site modules each include a line transformer 22, an audio line amplifier 23, and a threshold amplifier and relay switch package 24. Audio frequency signals transmitted from the protected station over the transmission lines 12 are coupled through the line transformer 22 to the audio amplifier 23 which amplifies the audio frequency signal. The line amplifier 23 may include one or more audio stages as needed, Parallel outputs from the line amplifier are taken off by means of adjustable potentiometers-ii and 49. The potentiometer 48 is a volume control potentiometer and the audio signal taken therefrom is fed simultaneously to fixed contacts on the first and second decks of the three deck rotary selector switch 17. The audio signal from a particularly numbered site module is fed to correspondingly numbered fixed contacts on the firstand second decks of the switch 17. That is, the audio output from site module 5 is fed to the fixed contacts 5 on the first and second switch decks, the audio output from site module 4 is fed to the 4' fixed contacts on the firstand second switch decks, and in like manner the audio outputs from the other side modules 3, 2 and I are fed to fixed contacts 3, it 2 and 1 on the first and second switch decks respectively.

The switch deck 1 includes an annular conductor ring 50 having an arcuate lateral projection which engages the fixed contacts 1-10 on the switch deck in sequence. A brush 52 contacts the conductor ring 50 at all times and transmits any signal picked off by the arcuate segment 51 from a particular numbered fixed contact to an amplifier 27 which feeds the signal to the individual loud speaker 16. It will therefore be seen by examination of the switch deck 1 that only the audio signal from one site module and thus from one protected station can be fed to the individual speaker 16 in any one ,position of the selector switch 17 thus the operator at the monitor station 14 is able to monitor the sound and audio alarm signals derived from a selected remote station.

The switch deck 2 includes an arcuate rotary conductor segment 54 which lacks being a complete circle by a short gap 55 of length less than the distance segment. The fixed contacts 1-10 are all provided with means for wiping the arcuate segment 54. A brush 56 connected with the amplifier 26 is also in contact with the rotary conductor segment 54 and will transmit any signal being picked up by the rotary segment 54 from the fixed contacts 2-10 wiping the segment 54 to the amplifier 26. The amplifier 26 amplifies the audio alarm signals present and drives the master loud speaker 15 with the amplified audio signals. Since the conductor segment 54 is in contact with all of the fixed contacts 1-10 except the one where the gap 55 occurs it will be seen that all signals from the site modules 47 connected to the switch deck 2 will be sampled simultaneously except for the signals from the site module 47 connected to fixed contact adjacent gap 55. In the position of the selector switch 17 shown the gap 55 is adjacent contact 1, thus the signal from site module 1 is not being picked up by the master speaker 15. However, turning now to switch deck 1 it will be observed that any signals from site module 1 are being transmitted from contact 1 through the arcuate segment 51 conductor ring 50, and brush 52 to the amplifier 27 from which the audio signals are applied to the individual speaker 16.

The switch deck 3 of the selector switch 17 is provided so that an energizing circuit through an audible buzzer may be put in a ready condition by switching the selector switch 17 to a standby position which is just to the right, or counterclockwise from the fixed contact 1. The deck 3 includes an annular rotary conductor 57 which has a lateral arcuate projection 58 and multiple fixed contacts equally spaced in a circle about the rotary conductor 57'. The fixed contacts numbered 1-10 are vacant and thus have no electrical function in thesystem. The two contacts a and b to the right of the fixed contact i have conducting means for engaging the arcuatesegrnent 58; they also are electrically tied together by a conductor 60 and are connected to one side of a buzzer 65, a capacitor 66 and a resistor 67 which are parallel connected between conductor 60 and ground. A brush 59 which engages the rotary conductor 57 is connected to the fixed contact c just clockwise of the numbered contact 10. When the selector switch 17 is turned counterclockwise off of the fixed contact 1 it is placed in a standby position wherein the arcuate segment 58 is in electrical contact with the fixed contact a and an electrical circuit is completed from ground through the buzzer 65 fixed contact a, segment 58, conductor ring 57, brush 59, diode D1 to the bottom side of parallel alarm indicator lamps 18 whose function will be subsequently described. Looking to switch decks 1 and 2, when the selector switch 17 is moved to the standby position arcuate segment 51 is moved counterclockwise off contact 1 so that none of the site modules 47 will be connected through deck 1 to the individual speaker 16. The gap 55 in rotary conductor 54 will be moved from position over contact 1 to a position over contact a and the conductor segment 54 will contact all of the fixed contacts to which the site modules 1-5 are connected.

1 Thus in the standby position all of the protected areas 10 will be monitored by the master speaker 15 through switch deck 2 while none of the protected areas 10 will be monitored by the individual speaker 16. 1f the 5 selector switch 17 is moved one more position counterclockwise so that segment 58 on deck 3 engages contact b the circuit from the bottom of lamps 18 ever since the brush 56 on deck 2 is connected to contact b and the gap 55 will now overlie the brush 56 none of the protected areas can be monitored by the master speaker. in deck 1 the segment 51 will be .over contact b to which brush 52 isconnected but none of the site modules will be'connected to the conductor ring 50 and therefore no signals from any of the protected areas will be monitored by the individual speaker.

Referring back to the site module 5 it will be seen that a portion of the audio output signal from amplifier 23 is tapped off by the sensitivity adjust potentiometer 49 and is fed into a threshold amplifier and relay switch package 24. This package 24 which will be discussed in greater detail with reference to FIG. 7 controls the sound operated relay switch 68 so that the switch 68 closes when the audio level of signals from the amplifier 23 exceeds a predetermined threshold level determined by the position of the adjustable sensitivity potentiometer 49. As seen in FIG. 4 each of the site modules includes a sound operated relay switch 68. One side of each relay switch 68 is connected to a 6.3 volt AC bus supplied from a grounded 6.3 volt AC power supply seen in FIG. 5.

The other side of each relay switch 68 is separately connected in series with one of the multiple parallel connected indicator lamps 18, and diode D2 to ground. Thus when one of the sound operated relay switches 68 provides power for all site modules 47 and the amplifiers 26 and 27; the 6.3 volt AC supply rated at 2 am-,

I peres' provides power to energize the visual indicator is closed in response to a signal received from a protected station 10 one of the indicator lights 18 will be energized. Each of the indicator lights are numbered to correspond to the number assigned to the protected station with which it is associated sothat an operator at the central monitor station can determine from the lighted indicator lamp which protected station is sending an alarm signal. The circuits for the indicator lamps 18 do not go through the selector switch 17 so the indicator lamp will signal upon actuation of an associated sound operated relay switch irrespective of the position of the selector switch.

The audible buzzer 65 is intended to give an audible alarm signal to the operator at the central station only when the selector switch 17 is in a standby position and any one of the sound operated relays closes in response to an alarm signal from a protected statiomThe operator being advised that an alarm condition exists by means of the audible sound from buzzer 65 can determine from observation of the visual alarm lamps 18 which station is sending the alarm. The operator will then switch the selector switch 17 to a position corresponding to the protected station sending the alarm. The operator then will be able to monitor the sound originating at the station to which the selector switch is FIG. 5 and includes a regulated 12 volt DC supply 70, a

6.3 volt AC supply 71 and a regulated 91 volt DC supply 72. These supplies are of conventional construction and need not be further described in detail except i i to say that the power supplies are energized from a 1 17 volt AC source 73 through appropriate sections of a transformer 74. The, 12 volt DC supply rated at 625 ma lamps 18; and the 91 volt DC supply rated at ma provides power for the neon lamps 31 and for activating the relays 39 in the remote stations 10.

The circuits shown in FIG. 6 are provided so that an operator at the monitor station 14 can observe and test the operative condition of the equipment at the protected stations 10 and the continuity of transmission lines 12. Neon lamps 31 (there being one for each protected station numbered in accord with the number of the protected stations with which a particular lamp is associated) are mounted on the instrument panel 14a (see FIG. 2) within view of the operator at the monitor station. Beside each neon lamp 31 is a push button test switch 46 also associated with a particular protected station. The parallel neon lamps 31 each with an associated voltage dropping resistor 76 in series with the power supply 72 and with a shunting resistor 75 are connected through separate conductors shown broken away at X1, X2, X3, X4 and X5 respectively to similarly marked conductors shown in FIG. 4 and to the center taps 22' on the primary windings of the line transformers 22 in particular site modules with which the individual lamps are associated. The neon lamp circuits are completed through associated transmission lines 12, conductors 41, transformer primary 37b, relay coil 39 and activate switch section 3017 in the remote station 10. When theactivate switch-30 is closed in a particular remote station 10 and the circuits between the indicator lamps 31 and the activate switch 30 are continuous the lamp 31 associated with the particular remote station 10 will light indicating the integrity of the circuits and that the set in the protected station 10 g is activated. The current flowing through the neon lamps 31 and resistors 75 and 76 will normally be insufficient to energize the relay 39 in the remote station. The parallel test switches 46 in series'with resistor 77 and the 91 volt DC power supply 72 are connected to power supply 28 and the audible noise generator 40 in the remote station is completed. The noise generator 40 will then sound and the noise willbe picked up by microphones 20 and transmitted as an alarm test signal to the monitor station. if the test signal is received at the monitor station 14 in the normal manner the operator at the monitor station will be assured that the equipment at the remote station and at the monitor station associated with the particular remote station being tested is in operative condition. If the test signal is not received at the monitor station in the normal manner the operator will know that equipment associated with the particular remote station being tested is impaired and can take appropriate corrective action.

A detailed schematic of typical circuitry within a site module 47 is shown in FIG. 7. The basic components of a site module are indicated in the site module 5 shown in FIG. 4 as being a line transformer 22, an I audio line amplifier 23, a threshold amplifier and relay switch package 24 and the sound operated relay switch 68. Each of these components are individually of substantially conventional design and various circuits capable of performing the same function as has been described for the basic components may be substituted within the scope of this invention. Thus while the circuits of a typical site module are shown in FIG. 7 this invention is not limited to the details of the circuits shown in FIG. 7.

Since each site module 47 is a self contained unit which can be readily interchanged with identical units in the event of malfunction, FIG. 7 shows all connecting terminals for the unit on the left hand side. ltwill be understood that these terminals are associated with a suitable connector so that the site module unit may be quickly connected and disconnected as need arises. The transmission lines 12 from a remote station are connected to the input terminals 3 and and these terminals are connected internally to opposite sides of the primary winding of line transformer 22. Terminal 2 is connected to the 91 volt DC supply 72 in the power supply unit shown in FIG. 5. Audio signals coupled through the line transformer are fed to the audio line transformer 23 which includes a transistor amplifier Q1 of the type 2N1305 operating Class A. Output signals from the emitter of transistor Q1 are taken off from adjustable gain and sensitivity potentiometers 48 and 49 connected in parallel. The audio output from gain potentiometer 48 is fed through a coupling capacitor '78 to the base of a second stage amplifier Q2 also of type 2N13l5 and operating in Class A. The second stage amplifier O2 further amplifies the audio signal taken from the gain potentiometer and feeds the audio output through coupling capacitor 79 to output terminal 1 from which it is fed by-suitable conductor means to the numbered fixed contacts on the decks l and 2 of the selector switch 17 corresponding to a particular numbered site module. The output from the sensitivity adjust potentiometer is fed through a coupling capacitor to the threshold amplifier O3 in the threshold amplifier, relay switch package generally indicated by the arrow 24. The amplifier O3 is a transistor amplifier type 2N3638 operating Class A for further amplifying the audio signal taken from the sensitivity potentiometer 49. The output from amplifier O3 is coupled through capacitor 81 to the transistor detector ()4 which produces a DC output corresponding to the voltage level of the audio signal. The output from detector Q4 is used to trigger the transistor switch Q5 which is in series circuit with the relay coil 68 of the sound operated relay switch 68. When the transistor switch Q5 is triggered on by an audio signal of a selected threshold level current flowing through the transistor Q5 will also flow through the relay coil 68' causing the relay switch 68 to close. One side of the relay switch 68 isconnected to the 6.3 volt AC bus through terminal 6. And the other side of switch 68 is connected to an indicator light 18 through terminal 7. As previously explained the closing of relay switch 68 will cause the indicator light 18 associated with a particular site module to light. The sensitivity, or audible threshold level of the sound operated relay 68 is ad justed by means of the sensitivity potentiometer 49. Sounds picked up by the microphones in the protected area 10 which are below a predetermined threshold level will not cause the sound operated relay 68 to operate. However sounds above the predetermined threshold level will trigger the transistor switch QS and closeithe sound operated relay switch 68 thus providing an alarm signal through a visual indicator lamp 18 and if the central monitor is in standby condition will cause the audible buzzer alarm 65 to sound.

The terminals 8 and 9 of the site module are connected to the 12 volt DC bus in the power supply and to ground respectively. Normally the threshold amplifier sensitivity potentiometer 4-9 will be adjusted so that a minimum signal of 20 db is required to close the relay switch 68. Transistors Q4 and OS are of type 2N3638.

FIG. 8 shows typical circuitry suitable for the individual speaker 16 and speaker amplifier 27 as well as for the master speaker 15 and master speaker amplifier 26. This circuitry is of conventional design whose function will be obvious to one with ordinary skill in the art for which reason a detailed description thereon will be omitted. However, depending on whether the circuit is used in conjunction with the individual speaker or the master speaker, both using similar circuitry, audio signals from the selector switch are fed through a volume control potentiometer 9t and coupling capacitor 91 to an audio amplifier module 92. The output from amplifier module 92 is fed to the primary 93 of transformer T1. Balanced outputs are taken from the secondary transformer coils 94 and 95 and fed as inputs to the loudspeaker driver amplifiers O6 and Q7. The driver amplifiers Q6 and Q7 are type 2N2869 transistors which are connected to drive a loudspeaker which may be either the individual speaker 16 or the master speaker 15 as the case may be.

The operation of my alarm system which it is believed will be understood from the foregoing description will be briefly summarized.

A central monitor station 14 is connected to plural remote protected stations It) by transmission lines 12 and is adapted to receive audio frequency signals from the protected stations. The audio signals may merely be derived from sound pickup microphones 20 within the protected stations 10 or may be obtained from abnormal condition sensing devices and encoders such as the tire, temperature, other, and burglary encoders 33,34, 35 and 36 shown in FlG. 3. The abnormal condition sensing devices which are energized from the 6 volt battery 28' are emergency items which are intended to be operative at all times especially when the activate switch 38 is open and the sound pickup system is off. Each remote station 10 must close an activate switch 30 in order to put the, premises under the sound surveilance of the central monitor station. Normally the activate switch will be closed at times when normal use and occupation of the building is not anticipated such as in the case of an office at the close of a business day. Closing the activate switch 30 energizes the audio amplifier 21 and pickup microphones 20.

In the central monitor station an attendant will normally be on duty in the vicinity of the instrument panel 14a shown in FIG. 2. The attendant will usually keep the selector switch 17 in a standby position as indicated in H6. 2, where the rotary dial knob 63 is turned so that the pointer 64 is in one of two positions, a or b, counterclockwise of the first site position 1. In the standby position a the attendant at the monitor station sound to further attract the operators attention. The

operator may then turn the selector switch indicator dial 63 so that the pointer 64 points to the number of the station from which the alarm signal is being sent. The individual speaker 16 will then be connected through deck 1 of the selector switch 17 to the output of an audio amplifier 23 in the site module of the selected station and audio signals coming from the selected station will be monitored by the individual speaker 16 to the exclusion of all other stations. However, any sounds from the other stations will be monitored by the master speaker simultaneously through switch deck 2 of the selector switch. The buzzer65 will be turned off as soon as the selector switch 17 is turned to point to a particular site number, but the visual indicator lamps 18 will be in ready condition at all times irrespective of the position of the selector switch 17. The attendant at the monitor station can adjust the volume of sound from the speakers 15 and 16 by means of volume control knobs 100 and 101 respectively on the instrument panel 140. These knobs control the gain potentiometer 90 of identical audio amplifiers 26 and 27 respectively as shown in FIG. 8.

The attendant can also observe which remote stations are activated by means of the lamps 31 which will be energized as soon as the activate switch 30 in protected stations are closed. A lighted lamp 31 means that a station 10 associated with the lamp is activated. if a lamp 31 is not lighted the associated remote station is either not activated or there is a malfunction. The attendant can test the sound monitoring system of a particular station It! by depressing an associated test switch 46 which will energize a noise generator in an activated remote station which sound will be picked up in the remote station by microphone and transmitted to the monitor station 14 provided the audio monitoring system is functioning properly. If no sound is received the attendant knows that a malfunction associated with the particular station being tested exists.

The reason for providing the condition encoders 34, 35 and 36 with different code patterns is so that the monitoring attendant can identify the particular abnorrnal condition being detected and take appropriate action.

it is preferred that the audible noise generator 40 described in reference to FIG. 1 and the audible buzzer 65 described in reference to FIG. 4 be an electronic audible signal generator of the type manufactured and sold under the trademark SONALERT by P. R. Mallary and Co., inc. and described in the two page specificaits circuitry is all solid state with the consequent low current requirements. With reference to FIG. 4, the 6.3

volt AC through lamps 18 is fed to the rectifiers D1 and D2 and is filtered by'condenser 66. The resistor 67 determines the amount of voltage to be rectified for the Sonalert 65 from the 6.3 volt AC applied to the indicator lights 18. The current consumption of the Sonalert will be very low.

Again with reference to FIG. 6 the resistors 75 and 76 associated with the neon lamps 31 are provided to simulate transmission line leakage of a minor nature.- Otherwise the neon lamps 31 would fire withmost any high resistance line leakage to ground. The neon lamp circuits use the ground path to return.

it should be recognized that while for convenience and simplicity in illustrating the invention only five remote protected stations have been shown and a selector switch with only ten site positions has been shown; it will be understood that the system is not limited to a specific number of remote protected stations as long as a selector switch with sufficient positions to handle the desired number of remote stations can be obtained.

While in the foregoing there has been described and shown the preferred embodiment of the invention, various modifications and equivalents may be resorted to within the spirit and scope of the invention as claimed.

What is claimed is:

1. An electrical alarm system, comprising a plurality of protected stations and a remote monitoring station connected to all of the protected stations by transmission lines, each of the protected stations including a condition sensing device capable of transmitting a signal. along said lines to said monitoring station when an abnormal condition exists at the protected station, a master signal detector provided at the monitoring station and simultaneously monitoring the sensing devices of all the protected stations, an individual signal detector at the monitoring station, and a selector switch at the monitoring station for transferring from said master detector to said individual detector an abnormal condition signal originating at any particular protected station, whereby that particular protected station may be monitored by the individual detector in exclusion of all the other protected stations which continue to be monitored by said master detector.

2. The system as defined in claim 1 together with a plurality of indicator lamps provided at said monitoring station and energizable by abnormal condition signals from the respective protected stations, said selector switch being manually actuated and having a plurality of settirigs'corresponding to the respective protected stations, whereby an abnormal condition signal from a particular protected station as indicated by its respective lamp may be transferred from said master detector to said individual detector by an appropriate setting of said manually actuated selector switch.

3. The system as defined in claim 1 which is further characterized in that said condition sensing device of at least one of the protected stations is responsive to sound and transmits an abnormal condition signal to said monitoring station when sound at that protected station reaches a predetermined threshold level.

4. The system as defined in claim 1 which is further characterized in that said condition sensing device of at least one of the protected stations is responsive to temperature and transmits an abnormal condition signal to said monitoring station when temperature at that protected station reaches a predetermined degree.

5. The system as defined in claim I which is further characterized in that said condition sensing device of at least one of the protected stations is responsive to a manually actuated switch and transmits an abnormal condition signal to said monitoring station when said last mentioned switch is actuated,

6. An electrical alarm system comprising a plurality of protected stations and a central monitor station connected to all of the protected stations by transmission lines, each of the protected stations including means for producing audio frequency electrical signals, and means for coupling said audio frequency electrical signals to said transmission lines for transmission to said central monitor station; said central monitor sta tion including a master loudspeaker for simultaneously monitoring the audio signals from all of the protected stations, an individual loudspeaker for individually monitoring the audio signals from only one protected station at one time, a multiposition selector switch, said selector switch having a standby position, means at said standby position for connecting audio frequency signals from all of said protected stations to said master loudspeaker while excluding all the audio frequency signals from said individual loudspeaker, a plurality of site positions corresponding in number to the number of protected stations, means ateach of said site positions for singly connecting audio frequency signals from the protected station corresponding to said selected site position to said individual loudspeaker and for simultaneously connecting the audio frequency signals from all of the protected stations exclusive of the selected protected station to said master loudspeaker, and means provided at said monitoring station for coupling the audio frequency signals from each of said protected stations to said rnultiposition selector switch. I i V 7. The apparatus set forth in claim 6 wherein said audio frequency producing means at each of said protected stations includes at least one sound transducer for picking up sounds produced in the region of the protected station.

' 8. The apparatus set forth in claim 7 wherein said audio frequency producing means also includesan audio frequency oscillator, and at least one means for keying said oscillator when an abnormal condition occurs in said protected station.

9. The apparatus set forth in claim 8 wherein there are plural diverse means for keying said oscillator, each keying means being responsive to a different abnormal condition and keying said oscillator in accordance with a preselected code indicative of the abnormal condition to which said keying means responds.

10. The apparatus set forth in claim 9 wherein at least one of said keying means includes a rotary periodic switch encoder in circuit with an abnormal condition sensing switch and a power supply for energizing said oscillator, said abnormal condition sensing switch being normally open in the absence of an abnormal condition and being closed upon the occurrance of an abnormal condition whereupon energy from said oscillator power supply is intermittently applied to said oscillator through said encoder in accordance with a predetermined code pattern.

11. The apparatus set forth in claim 7 wherein said sound transducer is a microphone and wherein said means for coupling said audio frequency signals from said sound transducer to said transmission lines is a coupling transformer having a centertapped secondary winding, each protected station further having an audio amplifier interposed between said microphone and said coupling transformer, a power supply for energizing said audio amplifier and microphone, an audio noise generator in circuit with said amplifier power supply and a normally open relay switch, said normally open relay switch having an energizing coil in circuit between said center-tapped secondary winding and ground, said monitor station further having a grounded power source for energizing the coil of said relay switch in each remote station through said transmission lines and circuit means for separately connecting said grounded power source to the transmission lines between each protected station and said monitor station including a test lamp means in each circuit means for indicating the operative condition of the protected station, and a test switch means paralleling said test lamp for applying a sufficient energy from said grounded power source to said relay coil when said test switch is closed to activate said relay switch whereupon said noise generator is energized to produce sound in said protected station which is picked up by said sound transducer and monitored in said monitor station.

12. The apparatus set forth in claim 6 together with a plurality of indicator lights at the monitoring station, there being one indicator light for each protected station, separate audio frequency signal responsive means at said monitoring station for each protected station for energizing the indicator light associated with a particular protected station when an audio frequency signal above a preselected threshold level is received and for deenergizing said indicator light when the audio frequency signal falls below said threshold level.

13. The apparatus set forth in claim i2. together with an audible alarm in normally open circuit with all of said indicator lights, said multiposition selector switch having means at said standby position for closing said normally open circuit between said audible alarm and said indicator lamps so that said audible alarm will sound whenever one of said indicator lights is energized.

14. The apparatus set forth in claim 6 wherein said selector switch is a rnultideck rotatable switch having multiple equally spaced fixed contacts circularly arranged on each deck, one deck having an annular rotatable conductor of smaller diameter than the inside diameter of the circle of contacts in said one deck, an arcuate segment extending radially outwardly from said annular conductor for separatelyengaging one of the fixed contacts at a selected position of said selector switch, a fixed brush in continuous engagement with said annular conductor and circuit means connected to said brush for transmitting signals from said brush to said individual loudspeaker, the fixed contacts of said one deck at said site positions being individually con nected to receive audio frequency signals from one of v the protected stations so that when said arcuate segmerit engages any one of the fixed contacts in said plural site positions, audio frequency signals appearing at the selected site position will be applied through said annular conductor and said brush to said individual speaker, a second deck having an annular rotary conductor interrupted by a narrow gap of arcuate length less than the distance between two adjacent fixed contacts on said second deck, means associated with each fixed contact in the site positions of said selector switch for wiping said interrupted annular conductor, a fixed brush in engagement with said interrupted annular conductor and circuit means connected to the fixed brush on said second deck for transmitting signals from said brush to said master loudspeaker, the fixed contacts on' said second deck at said site positions each being individually connected to receive audio frequency signals from one of the" protected stations, the gap on said interrupted annular conductor being in the same angular position as the arcuate segment extending from the annular conductor on said first deck so that when said selector switch is in a standby position the annular conductor on said second deck will be in conductive contact with all of the fixed contacts in the site positions, and the annular conductor on said first deck will be out of conductive contact with all of the fixed contacts in the site positions, and when said selector switch is in one of the site positions only the fixed contact at the selected site position on the first check will be in conductive contact with the annular conductor of the first deck, and all of the fixed contacts of all of the site positions except the selected site position on said second deck will be in conductive contact with said interrupted annular conductor on said second deck.

15. The apparatus set forth in claim 14 together with a plurality of indicator lights at the monitoring station, there being one indicator light for each protected station, separate audio frequency signal responsive means at said monitoring station for each protected station for energizing the indicatorlight associated with a particular protected station when an audio frequency signal above a preselected threshold level is received and for deenergizing said indicator light when the audio frequency signal falls below said threshold level, an audible alarm in normally open circuit with all of said indicator lights, said multiposition selector switch having a third deck and means provided on the third deck only at a standby position for closing said normally open circuit between said audible alarm and said indicator lights so that said audible alarm will sound whenever one of said indicator lights is energized.

16. The apparatus set forth in claim 6 wherein said coupling means at said monitor station for coupling the audio frequency signals from each protected station to said multiple position selector switch is included in a site module, there being plural separate site modules corresponding in number to the number of protected stations, each site module having a coupling transformer, an audio amplifier, and means connecting the output of said audio amplifier to a particular site position on said multiple position selector switch, said coupling transformer coupling the audio signals transmitted over the transmission lines from a particular remote station to said audio amplifier wherein the audio signals are amplified.

17. The apparatus set forth in claim 16 together with a plurality of indicator lights at the monitoring station, there'being one indicator light for each protected station, electric power means for energizing said indicator lights, and audio signal responsive means in each site module for energizing the indicator lights associated with a particular protected station when an audio frequency signal above a preselected threshold level is from said threshold amplifier, a sound operated relay means for opening and closing the energizing circuit to a particular indicator light, and means responsive to the d.c. output from said detector means for energizing 

1. An electrical alarm system, comprising a plurality of protected stations and a remote monitoring station connected to all of the protected stations by transmission lines, each of the protected stations including a condition sensing device capable of transmitting a signal along said lines to said monitoring station when an abnormal condition exists at the protected station, a master signal detector provided at the monitoring station and simultaneously monitoring the sensing devices of all the protected stations, an individual signal detector at the monitoring station, and a selector switch at the monitoring station for transferring from said master detector to said individual detector an abnormal condition signal originating at any particular protected station, whereby that particular protected station may be monitored by the individual detector in exclusion of all the other protected stations which continue to be monitored by said master detector.
 2. The system as defined in claim 1 together with a plurality of indicator lamps provided at said monitoring station and energizable by abnormal condition signals from the respective protected stations, said selector switch being manually actuated and having a plurality of settings corresponding to the respective protected stations, whereby an abnormal condition signal from a particular protected station as indicated by its respective lamp may be transferred from said master detector to said individual detector by an appropriate setting of said manually actuated selector switch.
 3. The system as defined in claim 1 which is further characterized in that said condition sensing device of at least one of the protected stations is responsive to sound and transmits an abnormal condition signal to said monitoring station when sound at that protected station reaches a predetermined threshold level.
 4. The system as defined in claim 1 which is further characterized in that said condition sensing device of at least one of the protected stations is responsive to temperature and transmits an abnormal condition signal to said monitoring station when temperature at that protected station reaches a predetermined degree.
 5. The system as defined in claim 1 which is further characterized in that said condition sensing device of at least one of the protected stations is responsive to a manually actuated switch and transmits an abnormal condition signal to said monitoring station when said last mentioned switch is actuated.
 6. An electrical alarm system comprising a plurality of protected stations and a central monitor station connected to all of the protected stations by transmission lines, each of the protected stations including means for producing audio frequency electrical signals, and means for coupling said audio frequency electrical signals to said transmission lines for transmission to said central monitor station; said central monitor station including a master loudspeaker for simultaneously monitoring the audio signals from all of the protected stations, an individual loudspeaker for individually monitoring the audio signals from only one protected station at one time, a multiposition selector switch, said selector switch having a standby position, means at said standby position for connecting audio frequEncy signals from all of said protected stations to said master loudspeaker while excluding all the audio frequency signals from said individual loudspeaker, a plurality of site positions corresponding in number to the number of protected stations, means at each of said site positions for singly connecting audio frequency signals from the protected station corresponding to said selected site position to said individual loudspeaker and for simultaneously connecting the audio frequency signals from all of the protected stations exclusive of the selected protected station to said master loudspeaker, and means provided at said monitoring station for coupling the audio frequency signals from each of said protected stations to said multiposition selector switch.
 7. The apparatus set forth in claim 6 wherein said audio frequency producing means at each of said protected stations includes at least one sound transducer for picking up sounds produced in the region of the protected station.
 8. The apparatus set forth in claim 7 wherein said audio frequency producing means also includes an audio frequency oscillator, and at least one means for keying said oscillator when an abnormal condition occurs in said protected station.
 9. The apparatus set forth in claim 8 wherein there are plural diverse means for keying said oscillator, each keying means being responsive to a different abnormal condition and keying said oscillator in accordance with a preselected code indicative of the abnormal condition to which said keying means responds.
 10. The apparatus set forth in claim 9 wherein at least one of said keying means includes a rotary periodic switch encoder in circuit with an abnormal condition sensing switch and a power supply for energizing said oscillator, said abnormal condition sensing switch being normally open in the absence of an abnormal condition and being closed upon the occurrance of an abnormal condition whereupon energy from said oscillator power supply is intermittently applied to said oscillator through said encoder in accordance with a predetermined code pattern.
 11. The apparatus set forth in claim 7 wherein said sound transducer is a microphone and wherein said means for coupling said audio frequency signals from said sound transducer to said transmission lines is a coupling transformer having a centertapped secondary winding, each protected station further having an audio amplifier interposed between said microphone and said coupling transformer, a power supply for energizing said audio amplifier and microphone, an audio noise generator in circuit with said amplifier power supply and a normally open relay switch, said normally open relay switch having an energizing coil in circuit between said center-tapped secondary winding and ground, said monitor station further having a grounded power source for energizing the coil of said relay switch in each remote station through said transmission lines and circuit means for separately connecting said grounded power source to the transmission lines between each protected station and said monitor station including a test lamp means in each circuit means for indicating the operative condition of the protected station, and a test switch means paralleling said test lamp for applying a sufficient energy from said grounded power source to said relay coil when said test switch is closed to activate said relay switch whereupon said noise generator is energized to produce sound in said protected station which is picked up by said sound transducer and monitored in said monitor station.
 12. The apparatus set forth in claim 6 together with a plurality of indicator lights at the monitoring station, there being one indicator light for each protected station, separate audio frequency signal responsive means at said monitoring station for each protected station for energizing the indicator light associated with a particular protected station when an audio frequency signal above a preselected threshold level is received and for dEenergizing said indicator light when the audio frequency signal falls below said threshold level.
 13. The apparatus set forth in claim 12 together with an audible alarm in normally open circuit with all of said indicator lights, said multiposition selector switch having means at said standby position for closing said normally open circuit between said audible alarm and said indicator lamps so that said audible alarm will sound whenever one of said indicator lights is energized.
 14. The apparatus set forth in claim 6 wherein said selector switch is a multideck rotatable switch having multiple equally spaced fixed contacts circularly arranged on each deck, one deck having an annular rotatable conductor of smaller diameter than the inside diameter of the circle of contacts in said one deck, an arcuate segment extending radially outwardly from said annular conductor for separately engaging one of the fixed contacts at a selected position of said selector switch, a fixed brush in continuous engagement with said annular conductor and circuit means connected to said brush for transmitting signals from said brush to said individual loudspeaker, the fixed contacts of said one deck at said site positions being individually connected to receive audio frequency signals from one of the protected stations so that when said arcuate segment engages any one of the fixed contacts in said plural site positions, audio frequency signals appearing at the selected site position will be applied through said annular conductor and said brush to said individual speaker, a second deck having an annular rotary conductor interrupted by a narrow gap of arcuate length less than the distance between two adjacent fixed contacts on said second deck, means associated with each fixed contact in the site positions of said selector switch for wiping said interrupted annular conductor, a fixed brush in engagement with said interrupted annular conductor and circuit means connected to the fixed brush on said second deck for transmitting signals from said brush to said master loudspeaker, the fixed contacts on said second deck at said site positions each being individually connected to receive audio frequency signals from one of the protected stations, the gap on said interrupted annular conductor being in the same angular position as the arcuate segment extending from the annular conductor on said first deck so that when said selector switch is in a standby position the annular conductor on said second deck will be in conductive contact with all of the fixed contacts in the site positions, and the annular conductor on said first deck will be out of conductive contact with all of the fixed contacts in the site positions, and when said selector switch is in one of the site positions only the fixed contact at the selected site position on the first check will be in conductive contact with the annular conductor of the first deck, and all of the fixed contacts of all of the site positions except the selected site position on said second deck will be in conductive contact with said interrupted annular conductor on said second deck.
 15. The apparatus set forth in claim 14 together with a plurality of indicator lights at the monitoring station, there being one indicator light for each protected station, separate audio frequency signal responsive means at said monitoring station for each protected station for energizing the indicator light associated with a particular protected station when an audio frequency signal above a preselected threshold level is received and for deenergizing said indicator light when the audio frequency signal falls below said threshold level, an audible alarm in normally open circuit with all of said indicator lights, said multiposition selector switch having a third deck and means provided on the third deck only at a standby position for closing said normally open circuit between said audible alarm and said indicator lights so that said audible alarm will sound whenever one of said indicAtor lights is energized.
 16. The apparatus set forth in claim 6 wherein said coupling means at said monitor station for coupling the audio frequency signals from each protected station to said multiple position selector switch is included in a site module, there being plural separate site modules corresponding in number to the number of protected stations, each site module having a coupling transformer, an audio amplifier, and means connecting the output of said audio amplifier to a particular site position on said multiple position selector switch, said coupling transformer coupling the audio signals transmitted over the transmission lines from a particular remote station to said audio amplifier wherein the audio signals are amplified.
 17. The apparatus set forth in claim 16 together with a plurality of indicator lights at the monitoring station, there being one indicator light for each protected station, electric power means for energizing said indicator lights, and audio signal responsive means in each site module for energizing the indicator lights associated with a particular protected station when an audio frequency signal above a preselected threshold level is received and for deenergizing said indicator light when the audio frequency signal falls below said threshold level.
 18. The apparatus set forth in claim 17 wherein said audio signal responsive means includes a threshold level adjusting means connected to the output of said audio amplifier for picking off a selected level of the audio output signal, a threshold amplifier connected to said threshold level adjusting means, a detector means for detecting the d.c. level of the audio output signal from said threshold amplifier, a sound operated relay means for opening and closing the energizing circuit to a particular indicator light, and means responsive to the d.c. output from said detector means for energizing said sound operated relay means when the d.c. level is above a certain level and for deenergizing said sound operated relay when said d.c. level is below a certain level. 